Abstract: :
Purpose: Light adaptation in the retina is known to involvechanges in levels of dopamine and nitric oxide, but the interactionsbetween these messengers remains unclear. Therefore we examinedthe effects of blocking D1 dopamine receptors on light-inducedincreases in nitric oxide production in the dark-adapted retina.Methods: Retinas from dark-adapted larval tiger salamanderswere isolated and sliced under infra-red optics, the slicesloaded with diaminofluorescein, washed, and transferred to light-tightboxes for stimulation. When appropriate, 15µM of the D1dopamine receptor antagonist SCH-23390 was included in the Ringers.Following stimulation, the slices were fixed in 4% paraformaldehydeand then the NO-induced fluorescence (NO-IF) was imaged usingconfocal microscopy.Results: Control, dark-adapted retinashad strong NO-IF in the OPL, concentrated in horizontal cellsomata and processes, but low levels in amacrine cells and theIPL. Flashing light (3Hz, 20µW, 660nm) increased NO-IFin numerous amacrine and ganglion cells. SCH23390 increasedthe NO-IF in unstimulated, dark-adapted slices but stronglydecreased the NO-IF stimulated by flashing light.Conclusions:Antagonism of D1 dopamine receptors altered NO-IF in both dark-adaptedand light-stimulated retinas. Blocking D1 receptors in the darkshifted the pattern of NO-IF to resemble that seen with lightstimulation, while blocking D1 receptors in the light shiftedthe pattern of NO-IF production towards the pattern seen inthe dark. This suggests that dopamine actively suppresses theproduction of NO in the dark-adapted retina and stimulates theproduction of NO in the light-adapted retina.